Refrigeration unit

ABSTRACT

A refrigeration unit applied, for example, to an air conditioning system for a car has a condenser, an expansion valve, and an evaporator interposed in a refrigerant circulation passage in the order named. The circulation passage includes a fluid-flowing area for a liquid refrigerant from the condenser to the expansion valve, and a gas-flowing area mainly for a gaseous refrigerant from the evaporator to the compressor. The refrigeration unit is provided with a detector for detecting the presence of the gaseous refrigerant in the liquid-flowing area. If the detector detects the gaseous refrigerant, a warning light indicative of a refrigerant leak is turned on.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a refrigeration circuit, and morespecifically to a refrigeration circuit for an air conditioning systemfor a vehicle, which is suitable for use of a flammable refrigerant withlow global warming potential.

2. Description of the Related Art

In late years, the development of an environment-friendly airconditioning system has been advanced. This air conditioning system hasa refrigeration circuit employing a refrigerant with low global warmingpotential. To be specific, refrigerants of this type include newalternatives for chlorofluorocarbon, such as R-152a, and HC gases, suchas propane.

Because of flammability of these gases, an air conditioning system ofthis type, especially a vehicle air conditioning system, is providedwith a gas sensor for detecting a leaked refrigerant in order to assurethe safety as disclosed, for example, in Unexamined Japanese PatentPublication No. 9-104221.

When the gas sensor is used, however, even in the event of a refrigerantleak, it is impossible to detect the leak unless the gas densityincreases in the vicinity of the gas sensor. For this reason, there isthe possibility that the sensor could not detect the refrigerant leak.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a refrigeration unitcapable of detecting a refrigerant leak without fail and warning theuser, the supervisor or the like.

In order to accomplish the above object, the refrigeration unit of thepresent invention includes a condenser, an expansion valve, and anevaporator interposed in a refrigerant circulation passage in the ordernamed, the passage having a liquid-flowing area for a liquid refrigerantfrom the condenser to the expansion valve, and a gas-flowing area mainlyfor a gaseous refrigerant from the evaporator to the compressor;detecting means for detecting presence of the gaseous refrigerant in theliquid-flowing area, said detecting means including a detector disposedin the liquid-flowing; and warning means for outputting a detectionresult when the detecting means detects the gaseous refrigerant. To beconcrete, for the detector, it is preferable to utilize a self-heatingtype thermistor, a pair of a light-emitting device and a light-receivingdevice or a microphone. The warning means preferably includes a warninglight or buzzer.

If a refrigerant leaked out from some place of the refrigerantcirculation passage, a refrigerant amount in the refrigerant circulationpassage decreases, which produces a gaseous refrigerant in theliquid-flowing area of the refrigerant circulation passage through whichthe liquid refrigerant is supposed to flow. Therefore, the presence ofthe gaseous refrigerant in the liquid-flowing area is an indexsignifying an occurrence of a refrigerant leak. Accordingly, in therefrigeration unit of the present invention, the detecting meansdetermines that there occurs a refrigerant leak in the refrigerantcirculation passage when a gaseous refrigerant is present in theliquid-flowing area of the refrigerant circulation passage, and thepresence of the gaseous refrigerant is detected by the detector. In thismanner, the detecting means reliably detects the refrigerant leak bydetecting the leak on the basis of the presence of the gaseousrefrigerant in the liquid-flowing area. Based on the detection resultgiven by the detecting means, the warning means warns the user,supervisor or the like of the refrigeration unit of the refrigerantleak.

In a preferred embodiment, a receiver is interposed in theliquid-flowing area, and the detector is disposed downstream from thereceiver. In this embodiment, in the event of a refrigerant leak, agaseous refrigerant is produced in the liquid-flowing area locateddownstream from the receiver. However, if the refrigeration unit isoperated in proper working order, the receiver removes the gaseousrefrigerant, so that the gaseous refrigerant is never present in theliquid-flowing area located downstream from the receiver. Consequently,the detector is prevented from making a false detection of a refrigerantleak when the refrigeration unit is in normal operation.

In a preferred embodiment, the refrigerant is a flammable refrigerant,for the flammable refrigerant generally has low global warming potentialand then is environment-friendly.

In a preferred embodiment, the refrigerant circulation passage runs froman engine room to a passenger compartment of a vehicle. If therefrigerant leaked, and the driver drove the vehicle without noticingthe leak, there would be a possibility that the engine or the like actsas a heat source to catch fire. According to the above-describedconfiguration, however, the driver is surely cautioned about therefrigerant leak, which assures the safety of the driver.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given hereinbelow and the accompanying drawingswhich are given by way of illustration only, and thus, are notlimitative of the present invention, and wherein:

FIG. 1 is a schematic view showing a configuration of a refrigerationunit according to one embodiment applied to an air conditioning systemfor a car;

FIG. 2 is a sectional view of a detector located in the refrigerationunit of FIG. 1;

FIG. 3 is a Mollier diagram for explaining the emergence of a gaseousrefrigerant in the event of a refrigerant leak in a liquid-flowing areaof a refrigerant circulation passage in the refrigeration unit of FIG.1;

FIG. 4 is a graph showing relation between temperature and electricresistance in a thermistor of FIG. 2;

FIG. 5 is a view showing a modification example of the detector of FIG.2; and

FIG. 6 is a view showing another modification example of the detector ofFIG. 2.

DETAILED DESCRIPTION

FIG. 1 is a schematic view showing a configuration of a refrigerationunit according to one embodiment applied to an air conditioning systemfor a car.

The refrigeration unit has a circulation passage 6 extending from anengine room 2 of a vehicle through a dash panel 3 to a passengercompartment 4, the circulation passage 6 being filled with R-152a asrefrigerant. A compressor 8 is interposed in a section of thecirculation passage 6 located in the engine room 2, and is activated bya driving force of an engine 10. The compressor 8 sucks the refrigerant,as a working fluid, in a phase of a low-pressure gas through a suctionport thereof, compresses the sucked refrigerant therein, and thendischarges the compressed refrigerant in a phase of high-temperature andhigh-pressure gas through a discharge port thereof. In short, thecompressor 8 creates a flow of the refrigerant in the circulationpassage 6 while compressing the refrigerant.

A condenser 12 is interposed in a section of the circulation passage 6downstream of the compressor 8 in the flowing direction of therefrigerant. The condenser 12 has an outer surface which receives airfrom the front of the vehicle and from a propeller fan (not shown), tothereby air-cool and condense the refrigerant flowing in the insidethereof.

A receiver 14 is also interposed in a section of the circulation passage6 downstream of the condenser 12. The receiver 14 separates an undesiredgaseous refrigerant remaining in the high-pressure liquid refrigerantthat has flowed in from the condenser 12, and causes only the liquidrefrigerant to flow out downstream.

An expansion valve 16 and an evaporator 18 each are interposed in asection of the circulation passage 6 in the order named, downstream ofthe receiver 14. The evaporator 18 is disposed in the passengercompartment 4. Specifically, an air conditioning unit housing (notshown) is disposed in an instrument panel 20 located in a front sectionof the passenger compartment 4. The air conditioning unit housingaccommodates the evaporator 18, a heater core, and a blower fan (notshown) together, which construct the air conditioning unit of the airconditioning system. The high-pressure liquid refrigerant from thereceiver 14 is supplied through the expansion valve 16 to the evaporator18, and is evaporated in the evaporator 18 to become a low-temperatureand low-pressure gaseous refrigerant. The downstream side of theevaporator 18 is connected to the compressor 8, so that the gaseousrefrigerant is sucked into the compressor 8. As to the expansion valve16, the valve opening thereof is automatically varied according to adegree of superheat of the refrigerant at the downstream side of theevaporator 18, thereby adjusting the degree of superheat into apredetermined range.

In the circulation passage 6, the compressor 8, the condenser 12, thereceiver 14, the expansion valve 16 and the evaporator 18 are connectedto each other by conduits 22.

The refrigeration unit has a self-heating type thermistor 26 as adetector 24 for detecting a refrigerant leak in the circulation passage6. The thermistor 26 is liquid-tightly fixed to the conduit 22connecting the receiver 14 and the expansion valve 16. A self-heatingresistance portion of the thermistor 26 projects into the conduit 22.The thermistor 26 is electrically connected to a control circuit 28located in the instrument panel 20. The control circuit 28 supplieselectric power to the thermistor 26 to cause the self-heating resistanceportion of the thermistor 26 to generate heat at a prescribed heatingvalue, and is capable of detecting electric resistance of theself-heating resistance portion of the thermistor 26.

The control circuit 28 is also electrically connected to a warning light30 provided to the instrument panel 20. When the electric resistance ofthe thermistor 26 is reduced to be lower than a prescribed lower limit,the control circuit 28 carries electricity to the warning light 30,thereby turning on the warning light 30.

According to the air conditioning system for the vehicle thusconfigured, the passenger compartment 4 is air-conditioned bycirculating the refrigerant through the circulation passage 6 during thenormal air-conditioning operation of the system. To be more specific,the compressor 8, when being activated upon receiving the driving forcefrom the engine 10, sucks the low-temperature and low-pressure gaseousrefrigerant from a return path of the circulation passage 6, compressesthe sucked gaseous refrigerant, and discharges the compressed gaseousrefrigerant to a feed path of the circulation passage 6. The dischargedrefrigerant passes the condenser 12 with the condensation from the phaseof high-temperature and high-pressure gas to the liquid phase. Therefrigerant in the liquid phase passes through the receiver 14 to theexpansion valve 16. The expansion valve 16 makes the refrigerant jetinto the evaporator 18 with the expansion of the refrigerant from theliquid phase to the gas-liquid mixing phase of low-temperature andlow-pressure and evaporate in the evaporator 18 while the valve openingthereof varies so that the degree of superheat of the refrigerant at theoutlet of the evaporator 18 falls within a given range. The refrigerantevaporated in the evaporator 18 is again sucked into the compressor 8.

In this circulation process of the refrigerant, once the blower fan ofthe air conditioning unit is activated, cold air from which evaporationheat has been removed by passing through the evaporator 18 is fed intothe passenger compartment 4. This cold air air-conditions the passengercompartment 4 at a desired preset temperature.

The air conditioning system for the vehicle thus configured employsR-152a with low global warming potential as refrigerant, thereby beingenvironment-friendly.

According to the air conditioning system for the vehicle thusconfigured, even if the refrigerant leaked out from some place of thecirculation passage 6, the warning light 30 is turned on to reliablywarn the driver, as an operator, of the refrigerant leak. Therefore, ifby any chance the R-152a that is a flammable refrigerant leaked out ofthe circulation passage 6, the driver certainly notices the refrigerantleak, thereby coping with the leak. Consequently, it is possible tosurely avoid the accident in which the engine 10 or the like acts as aheat source to catch fire, and the safety of the driver is assured.

More specifically, in the normal circulation process of the refrigerant,a portion of the circulation passage 6 which is located between thecondenser 12 and the expansion valve 18 forms a liquid-flowing areathrough which the high-pressure liquid refrigerant flows. The state ofthe refrigerant running through the liquid-flowing area is indicated bydot A in the Mollier diagram shown by a chain double-dashed line of FIG.3. Dot A is located within the supercooled liquid area that stretchesleftwards from a saturated liquid line. A portion of the circulationpassage 6 which is located between the evaporator 18 and the compressor8 forms a gas-flowing area through which the low-pressure gaseousrefrigerant flows.

Contrarily, if the refrigerant leaked out from some place of thecirculation passage 6, and a refrigerant amount within the circulationpassage 6 decreased, the refrigerant pressure lowers in theliquid-flowing area and yet rises in the gas-flowing area. A Mollierdiagram showing this condition is indicated by a solid line of FIG. 3.The state of the refrigerant running through the liquid-flowing area isshown by dot B on the Mollier diagram. Dot B is located within agas-liquid mixing phase area expanding between the saturated liquid lineand a saturated vapor line. Thus, if the refrigerant amount within thecirculation passage 6 decreased, the gaseous refrigerant graduallyincreases among the refrigerant flowing through the liquid-flowing areaof the circulation passage 6 through which the liquid refrigerant issupposed to flow. That is to say, the presence of the gaseousrefrigerant in the liquid-flowing area is an index signifying anoccurrence of a refrigerant leak in the circulation passage 6.

As to the detector 24 fixed to the liquid-flowing area of thecirculation passage 6, namely the self-heating type thermistor 26, theself-heating resistance portion thereof is supplied with electric powerfrom the control circuit 28 and generates heat at the prescribed heatingvalue, and at the same time loses its heat to the surroundingrefrigerant.

TABLE 1 below shows heat conductivity of the R-152a in liquid andgaseous phases at a temperature of 25 degrees centigrade. TABLE 1 PhaseHeat conductivity W/(m · K) Liquid phase 0.105 Gaseous phase 0.0136

As shown in TABLE 1, the R-152a of the liquid phase has almost about tentimes as great heat conductivity as the R-152a of the gaseous phase. Asa result, when the refrigerant amount within the circulation passage 6decreases, and the gaseous refrigerant starts getting mixed into theliquid-flowing area, an amount of heat taken from the self-heatingresistance portion of the thermistor 26 decreases, and the temperatureof the self-heating resistance portion rises. The temperature rise ofthe self-heating resistance portion, as diagrammatically shown in FIG.4, causes a reduction in electric resistance of the self-heatingresistance portion of the thermistor 26. In other words, a B-value and aC-value of the thermistor 26 are determined such that they satisfy anexpression; (the amount of heat taken from the self-heating resistanceportion by the gaseous refrigerant of a superheated gas area)<(theheating value of the self-heating resistance portion)<(the amount ofheat taken from the self-heating resistance portion by the liquidrefrigerant of the supercooled liquid area).

The electric resistance of the self-heating resistance portion of thethermistor 26 is measured and monitored by the control circuit 28. Whenthe electric resistance of the self-heating resistance portion becomessmaller than the prescribed lower limit, the control circuit 28determines that the state of the refrigerant is changed from thesupercooled liquid area to the gas-liquid mixing phase area. Thedetermination of the change into the gas-liquid mixing phase area meansthe determination of the presence of the gaseous refrigerant in theliquid-flowing area and of the occurrence of a refrigerant leak. Basedon the determination result of the occurrence of the refrigerant leak,the control circuit 28 carries electricity to the warning light 30 toturn it on, thereby warning the driver of the refrigerant leak.

The present invention is not limited to the above-described oneembodiment, and may be modified in various ways.

Although in the one embodiment, the receiver 14 is interposed betweenthe condenser 12 and the expansion valve 16, it is possible to interposean accumulator, instead of the receiver 14, between the evaporator 18and the compressor 8, and to utilize an orifice with a fixed opening, instead of the expansion valve 18. In this case, mainly the gaseousrefrigerant flows through the gas-flowing area lying between theevaporator 18 and the accumulator. Occasionally, since the degree ofsuperheat of the refrigerant at the outlet of the evaporator 18 is notcontrolled by the orifice, the liquid refrigerant which does notevaporate in the evaporator 18 also runs the gas-flowing area, albeitonly in small amount, and is reserved in the accumulator. Meanwhile, ifthe gaseous refrigerant that is accidentally not condensed by thecondenser 12 flows through the liquid-flowing area of the circulationpassage 6, this triggers false operation of the detector 24, resultingin a deterioration of detection accuracy with respect to a refrigerantleak. It is then preferable that the detector 24 be disposed downstreamof the receiver 14 as in the one embodiment.

Although the R-152a is used as refrigerant in the one embodiment,another chlorofluorocarbon (HFC gas) or HC gases, such as propane, maybe used instead.

In the one embodiment, the warning light 30 that visually attractsattention is used as warning means for the driver. The warning means,however, serves satisfactorily enough as long as it causes the driver tonotice a refrigerant leak clearly. Accordingly, as shown by a chaindouble-dashed line in FIG. 1, a warning buzzer 38 that auditorilyattracts attention may be utilized instead of or together with thewarning light 30.

Although in the one embodiment, the thermistor 26 is used as thedetector 24 for detecting the gaseous refrigerant in the liquid-flowingarea of the circulation passage 6, an optical detector 24 formed of alight-emitting device 32 and a light-receiving device 34 capable ofreceiving light from the light-emitting device 32 may be utilized asshown in FIG. 5. The light-emitting device 32 and the light-receivingdevice 34 are diametrically arranged on both sides of the conduit 22with respective transparent glass sheets 36 interposed therebetween. Thelight emitted from the light-emitting device 32 passes through the glasssheets 36 and the liquid refrigerant in the conduit 22, to thereby enterthe light-receiving device 34. When the light passes through the liquidrefrigerant, if bubbles of the gaseous refrigerant are included in theliquid refrigerant, the light is scattered due to the bubbles, whichdecreases the intensity of the light incident on the light-receivingdevice. Therefore, the control circuit 28 detects the decrease of theintensity of the light entering the light-receiving device 34, and turnson the warning light 30 if the decrease reaches a certain or higherlevel.

Moreover, as shown in FIG. 6, the detector 24 may be replaced with amicrophone 40. In this case, the presence of the gaseous refrigerant inthe liquid refrigerant is detected by detecting abnormal noises producedwhen the bubbles of the gaseous refrigerant are spouted from theexpansion valve 16 by means of the microphone 40.

It is noted that, in case that a pressure sensor is utilized as thedetector 24, a pressure decrease in the circulation passage 6 is modestuntil there remains scarcely any refrigerant in the circulation passage6, which makes it difficult to detect a refrigerant leak in earlystages. As a consequence, it is preferable that the thermistor 26 beused as the detector 24 as in the one embodiment.

Needless to say, the refrigeration unit of the present invention can beapplied not only to the air conditioning system for the vehicle but alsoto a room air conditioner, a refrigerator, and a freezer. In any case,the refrigeration unit warns the user, the supervisor or the like of arefrigerant leak without fail.

The invention thus described, it will be obvious that the same may bevaried in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

1. A refrigeration unit comprising: a condenser, an expansion valve, andan evaporator interposed in a refrigerant circulation passage in theorder named, the passage having a liquid-flowing area for a liquidrefrigerant from said condenser to said expansion valve, and agas-flowing area mainly for a gaseous refrigerant from said evaporatorto said compressor; detecting means for detecting presence of thegaseous refrigerant in said liquid-flowing area, said detecting meansincluding a detector disposed in said liquid-flowing area; and warningmeans for outputting a detection result when said detecting meansdetects the gaseous refrigerant.
 2. The refrigeration unit according toclaim 1, wherein: a receiver is interposed in said liquid-flowing area;and said detector is disposed downstream from said receiver.
 3. Therefrigeration unit according to claim 2, wherein: said detector includesa self-heating type thermistor.
 4. The refrigeration unit according toclaim 3, wherein: said refrigerant is a flammable refrigerant.
 5. Therefrigeration unit according to claim 4, wherein: said warning meansincludes a warning light.
 6. The refrigeration unit according to claim4, wherein: said warning means includes a warning buzzer.
 7. Therefrigeration unit according to claim 4, wherein: said refrigerantcirculation passage runs from an engine room to a passenger compartmentof a vehicle.
 8. The refrigeration unit according to claim 2, wherein:said detector includes a light-emitting device and a light-receivingdevice.
 9. The refrigeration unit according to claim 8, wherein: saidrefrigerant is a flammable refrigerant.
 10. The refrigeration unitaccording to claim 9, wherein: said warning means includes a warninglight.
 11. The refrigeration unit according to claim 9, wherein: saidwarning means includes a warning buzzer.
 12. The refrigeration unitaccording to claim 9, wherein: said refrigerant circulation passage runsfrom an engine room to a passenger compartment of a vehicle.
 13. Therefrigeration unit according to claim 2, wherein: said detector includesa microphone.
 14. The refrigeration unit according to claim 13, wherein:said refrigerant is a flammable refrigerant.
 15. The refrigeration unitaccording to claim 14, wherein: said warning means includes a warninglight.
 16. The refrigeration unit according to claim 14, wherein: saidwarning means includes a warning buzzer.
 17. The refrigeration unitaccording to claim 14, wherein: said refrigerant circulation passageruns from an engine room to a passenger compartment of a vehicle.